Admittedly rainbow dyed roses are pretty tacky, but the idea of "mutation" is cool. And the HowTo behind it seems simple enough. Pick Chur explains:

"In 2004, two dutch companies, River Flowers and F.J. Zandbergen, experimented and successfully grew a rose that had its petals rainbow colored. As petals get their nourishment through stem, the idea is to split the stem into several channels and dip each one in a different colored water. This way all the colors will be drawn by the stem into petals and resultant rose will have all the colors in it."